1. Technical Field
Embodiments relate to the manufacturing of a TiN/Ta2O5/TiN capacitor and more specifically to a method for reoxidizing the Ta2O5 layer after its forming on a TiN support.
2. Discussion of the Related Art
The use of TiN/Ta2O5/TiN-type capacitors has increased over the last years, especially on account of their compatibility with the manufacturing of the metallization levels of an integrated circuit and because, due to the high dielectric constant of Ta2O5, they can have high capacitances for small surface areas. Such capacitors are, for example, used to form the capacitors of DRAM-type memory cells, of radio frequency filters, or of analog-to-digital converters.
Among methods for forming such capacitors, a plasma enhanced atomic layer deposition method has been provided to form the Ta2O5 layer, this method presently called PEALD.
This method comprises alternating phases of tantalum deposition from a precursor, currently, the so-called TBTDET product, that is, tertbutylimido-tris-diethylamino tantalum, and phases of application of an oxygen plasma. Then, an upper TiN electrode is deposited by any adapted method.
Among the qualities which are expected from a capacitor, it is especially desired for it to have as low a leakage current as possible, preferably below 10−7 A/cm2. The dielectric relaxation factor is also desired to be reduced. This relaxation factor, FR, characterizes the capacitance variation of a capacitor according to frequency and is defined by relation FR=[C(1 kHz)−C(10 kHz)]/C. Thus, this factor characterizes the capacitance variation of a capacitor between an operation at a 1-kilohertz frequency and an operation at a 10-kilohertz frequency. Physically, this factor is linked to the presence of dipoles in the dielectric and to the relaxation time of these dipoles.
Various standards set the desired values of the relaxation factor. Present standards need for this relaxation factor to be, in percent, smaller than 0.2 for a capacitor operation at 25° C. and smaller than 0.6 for a capacitor operation at 125° C.
To obtain such leakage current characteristics and the dielectric relaxation factor, the applicant has provided:
all along the PEALD process, to limit the temperature within a range from 200 to 250° C.,
during the steps of tantalum deposition from TBTDET, limiting the partial TBTDET pressure within a range from 0.05 to 5 Pa, preferably from 0.5 to 2 Pa, preferably on the order of 1 Pa to within 10%, and
during phases of application of an oxygen plasma, limiting the partial oxygen pressure within a range from 1 to 2,000 Pa, preferably from 10 to 30 Pa, preferably to 25 Pa to within 10%.
The applicant has shown that this choice provides optimized results in terms of leakage current and of dielectric relaxation factor.
After the steps of forming of the Ta2O5 layer on a TiN support, it can be observed that there inevitably still remain defects, and especially oxygen vacancies.
To improve the state of the Ta2O5 layer, a reoxidizing is known to be desirable at the end of the process.
However, experience shows that reoxidations performed up to now provide very inhomogeneous results and can even alter some characteristics, especially the leakage current or the dielectric relaxation factor of the finally-obtained capacitor. Further, in the case of the integration of MIM (Metal-Insulator-Metal) structures at the level the interconnects of a circuit, the processing temperature must be lower than 400° C., or even lower than 350° C., to preserve the integrity of the interconnects.
There thus is a need to improve the reoxidizing process of a Ta2O5 layer in a capacitor of TiN/Ta2O5/TiN type.